CYTOLOGY

Fluid Compartments

Understanding the distribution of fluids in the body is essential for grasping cellular function and homeostasis.

• Extracellular Fluid (ECF): Fluid outside cells, including:

  • Plasma: The liquid component of blood.

  • Interstitial Fluid: Fluid between cells in tissues.

• Intracellular Fluid (ICF): Fluid within cells, comprising the majority of total body water.

Biological Membranes

Cell membranes regulate the movement of substances and maintain cellular integrity.

• Cell Theory: All living things are composed of cells; cells are the basic unit of life.

• Bilayer & Plasma Membrane: Composed of a phospholipid bilayer with embedded proteins.

• Membrane Composition: Includes lipids, proteins, and carbohydrates.

• Surface to Volume Ratio: Influences cell size and efficiency of transport.

• Fluid Mosaic Model: Describes the dynamic arrangement of lipids and proteins.

  • Peripheral Proteins: Attached to membrane surface.

  • Integral Proteins: Span the membrane.

  • Glycocalyx: Carbohydrate-rich area on cell surface, includes:

    • Glycolipids:

    • Glycoproteins:

• Selective Permeability: Membranes allow certain substances to pass while restricting others.

Cells

Cells are the fundamental units of life, each with specialized structures and functions.

• Cytoplasm: Gel-like substance inside the cell, containing organelles.

• Cytosol: Fluid portion of cytoplasm.

• Organelles: Specialized structures within cells, including:

  • Ribosomes: Made from protein or RNA proteins

  • Endoplasmic Reticulum (ER): Synthesis of proteins

  • Golgi Apparatus: Sorts, modifies and packages proteins into vesicles

  • Mitochondria: Essential role in cellular ATP production

  • Lysosome: break down bacteria and old organelles

  • Peroxisomes: break down fatty acids and toxic materials

  • Inclusions: Lipid droplets, glycogen granules and ribosomes

• Cytoskeleton: Network of protein filaments for structural support and movement.

  • Centrosomes: Aspherical structure in the cytoplasm

  • Motor proteins: Use ATP to create movement along cytoskeletal proteins

  • Nucleus: controls cellular activates

• Cell Junctions: Structures that connect cells to one another.

HISTOLOGY

Cell Junctions

Cell junctions maintain tissue integrity and facilitate communication between cells.

• Apical Surface: Exposed to the lumen or external environment; may have:

  • Cilia: Fluid movement across cells

  • Microvilli:

• Basal Surface: Attached to underlying tissue via the basement membrane.

• Lateral Surface: Connects adjacent cells through:

  • Tight Junctions: occluding junctions Anchoring junctions

  • Adhesive Junctions: maintain tissue integrity (zona)

  • Desmosomes: Bind adjacent cells together, helps keep cells from tearing apart

  • Gap Junctions: communicating junctions

Functional Categories of Tissues

Tissues are classified based on their structure and function.

Epithelial Tissues

• Exchange: Simple squamous epithelium allows rapid exchange of gases and nutrients.

• Transporting: Simple cuboidal and simple columnar epithelia facilitate absorption and secretion.

• Protective: Stratified squamous epithelium protects against abrasion; can be:

  • Keratininzed (skin)

  • Non-keratinized (oral cavity, esophagus)

• Secretory: Glandular epithelium forms glands:

  • Endocrine: (secretes hormones into blood)

  • Exocrine: (secretes substances into ducts)

  • Goblet cells: (secrete mucus)

Connective Tissues

• Loose Connective Tissue: Provides support and flexibility.

  • Areolar many structural components common to other connective tissues

  • Adipose Closely packed adipocytes, Have nucleus pushed to one side by fat droplet

  • Reticular Forms a soft, internal skeleton (stroma); Supports other cell types

• Dense Connective Tissue: Provides strength and resistance to stretching.

  • Regular Attaches muscle to bone; Attaches bone to bone; Withstands great stress in one direction

  • Irregular Withstands tension; Provides structural strength

  • Elastic Allows recoil after stretching (elastic fibers)

• Cartilage: Supports and cushions joints.

  • Hyaline : Supports and reinforces; Resilient cushion; Resists repetitive stress

  • Elastic Maintains shape of structure; Allows great flexibility

  • Fibrocartilage Tensile strength and ability to absorb compressive shock

• Bone: Rigid support and protection.

• Blood: Transports nutrients, gases, and wastes.

• Adipose Tissue: Stores energy as fat.

Muscle Tissues

• Skeletal Muscle: Voluntary movement.

• Smooth Muscle: Involuntary movement in organs.

• Cardiac Muscle: Heart contraction.

Nervous Tissues

• Neurons: Transmit electrical signals.

• Neuroglia: Support and protect neurons.

METABOLISM

Thermodynamics in Biology

Energy transformations in biological systems are governed by the laws of thermodynamics.

• First Law: Energy cannot be created or destroyed, only transformed.

• Second Law: Entropy (disorder) increases in spontaneous processes.

• Types of Energy:

  • Potential energy: stored energy

  • Kinetic energy: energy of movement

  • Entropy: measure of how many possible arrangements atoms in a system can have, often seen as its disorder or randomness

  • Exergonic reactions: (release energy)

  • Endergonic reactions: (require energy)

Metabolic Pathways

Metabolism encompasses all chemical reactions in the body, divided into two main types.

• Catabolism: Breakdown of molecules to release energy.

• Anabolism: Synthesis of complex molecules from simpler ones.

Enzymes

Enzymes are biological catalysts that speed up chemical reactions.

• Enzyme Naming: Often end with "-ase" (e.g., lactase).

• Activation Energy: Minimum energy required to start a reaction.

• Cofactors: Non-protein helpers (e.g., metal ions).

• Coenzymes: Organic cofactors (e.g., vitamins).

Cellular Respiration

Cellular respiration is the process by which cells generate ATP from nutrients.

• Overall Equation:

• Anaerobic Metabolism: Glycolysis (occurs without oxygen).

• Aerobic Metabolism: Citric acid cycle and electron transport chain (require oxygen).

• ATP Yield: Know the number of ATP produced by each pathway.

CENTRAL DOGMA OF MOLECULAR BIOLOGY

DNA

DNA stores genetic information and serves as a template for RNA synthesis.

• DNA Template: Used by RNA polymerase during transcription.

• Transcription Factors: Proteins that regulate gene expression.

• Gene Structure:

  • Promoter: Initiates transcription.

  • Constitutively active: Always expressed.

  • Regulated: Expression controlled by signals.

RNA

RNA is synthesized from DNA and translated into proteins.

• Splicing: Removal of introns and joining of exons.

• Post-transcriptional Processing: Modifications after RNA synthesis.

• Translation: mRNA template is used by ribosomes to assemble proteins.

• Codon: Three-nucleotide sequence specifying an amino acid.

• Amino Acid 'Alphabet': 20 standard amino acids.

• Post-translational Processing: Protein modifications after translation.

ADDITIONAL REVIEW

• Necrosis vs. Apoptosis: Necrosis is uncontrolled cell death; apoptosis is programmed cell death.

• ATP & ADP Structure: ATP (adenosine triphosphate) has three phosphate groups; ADP (adenosine diphosphate) has two.

• ATP Energy Storage: Energy is stored in phosphate bonds; released when ATP is hydrolyzed to ADP.

• ATP Synthesis: Energy for ATP synthesis comes from catabolism of nutrients.

• Electron Transport Chain Location: In eukaryotes, located in the inner mitochondrial membrane.

• Glycolysis vs. Cellular Respiration: Glycolysis yields less ATP than cellular respiration; compare energy yield per glucose molecule.

• Catabolic & Anabolic Reactions: Catabolic reactions break down molecules; anabolic reactions build molecules.

• Stepwise Metabolic Reactions: Metabolic pathways often occur in steps, each catalyzed by a specific enzyme.

• Enzyme Specificity: Enzymes are specific due to their active site structure.

• Nutritional Requirements: Humans require macronutrients (carbohydrates, proteins, fats) and micronutrients (vitamins, minerals).

Example Table: Comparison of Epithelial Tissue Types

Additional info: Academic context and examples have been added to expand upon the original study guide points and ensure completeness for exam preparation.